(a) Field of the Invention
An exemplary embodiment of the present invention relates to a method for generating feedback signal patterns of common feedback channels using a cyclic shift in a multiple access system and transmitting them to another party, and a transceiver therefore.
(b) Description of the Related Art
A current mobile communication system adopts a hybrid automatic retransmit request (HARQ) technology that changes a transmission scheme according to a state of a channel and a link adaptation technology of such adaptive modulation, etc., to obtain an additional performance gain.
In order to use the link adaptation technology, success or failure of decoding of data received from a receiver to a transmitter, channel state information, etc., should be fed back. In the case of unicast communication that transmits transmission packets to only one receiver, dedicated feedback channels should be allocated to each receiver. Since the transmitters and the receivers are each synchronized with each other, little inter-symbol interference or inter-subcarrier interference occurs even though receiving response signals to feedback signals are out of a cyclic prefix (CP) interval in the multiple access system using a plurality of subcarriers.
In the case of multicast communication that simultaneously transmits one packet to a plurality of receivers, only information on the worst channel state in all the groups receiving the same packets is needed. As a result, instead of an individual feedback allocation scheme that produces an excess feedback burden, a common feedback scheme, which shares the same physical resources and simultaneously transmits the feedback signals by several terminals, is considered.
As one example, a hybrid automatic retransmission request (HARQ) ACK/NACK common feedback scheme for multicast data will be described below. Herein, a base station is considered to be a transmitter and a terminal is considered to be a receiver.
The terminal receiving data transmits ACK (receive success) or NACK (receive failure) signals through the common feedback channels shared for the multicast groups in order to notify the base station of the success or failure of receipt. At this time, when the ACK or NACK signals are transmitted in general signal patterns, all the terminals sharing feedback resources are synchronized with each other such that if all the transmitted signals are received in the cyclic prefix, the inter-symbol interference or the inter-subcarrier interference does not occur. However, when there are some terminals that are not synchronized with each other, the occurrence of the interference cannot be excluded.
FIG. 1 shows an example of transmission signal configuration in common feedback channels according to a scheme of the related art.
As one example, when there is out-of-synchronization between the base station and the terminal, the case where the terminal is in an idle mode can be considered. In other words, when the terminal in the idle mode receives multicast services, the corresponding terminal does not maintain the uplink synchronization with the base station. Therefore, when the terminal transmits the feedback signals in the common feedback channels, the receive timing may deviate from the original receive timing. As shown in FIG. 1, when the time difference is out of the cyclic prefix, the inter-symbol interference and the inter-subcarrier interference occurs such that the receiving performance is degraded.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.